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Date:   Thu, 22 Jul 2021 20:55:30 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Boris Pismenny <borisp@...dia.com>
Cc:     dsahern@...il.com, kuba@...nel.org, davem@...emloft.net,
        saeedm@...dia.com, hch@....de, sagi@...mberg.me, axboe@...com,
        kbusch@...nel.org, edumazet@...gle.com, smalin@...vell.com,
        boris.pismenny@...il.com, linux-nvme@...ts.infradead.org,
        netdev@...r.kernel.org, benishay@...dia.com, ogerlitz@...dia.com,
        yorayz@...dia.com, Boris Pismenny <borisp@...lanox.com>,
        Ben Ben-Ishay <benishay@...lanox.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Yoray Zack <yorayz@...lanox.com>
Subject: Re: [PATCH v5 net-next 02/36] iov_iter: DDP copy to iter/pages

On Thu, Jul 22, 2021 at 02:02:51PM +0300, Boris Pismenny wrote:
> From: Boris Pismenny <borisp@...lanox.com>
> 
> When using direct data placement (DDP) the NIC writes some of the payload
> directly to the destination buffer, and constructs SKBs such that they
> point to this data. To skip copies when SKB data already resides in the
> destination we use the newly introduced routines in this commit, which
> check if (src == dst), and skip the copy when that's true.
> 
> As the current user for these routines is in the block layer (nvme-tcp),
> then we only apply the change for bio_vec. Other routines use the normal
> methods for copying.

Please, take a look at -rc1 and see the changes in lib/iov_iter.c in there.

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